For the sake of creating a workable model for emissions within Chapel Hill, it was important for us to isolate any confounding variables that may skew our data, to the best of our abilities.  In this regard, we decided upon the "Glass Box" model for Chapel Hill's carbon release.  In this model, an invisible glass box is assumed around the city.  Apart from several factors we have specified outside of this box, we are accounting only for the carbon released within this box as a direct result of activities that go on inside the box.  Our assumptions for this variable isolation are listed below:

1.    Chapel Hill is responsible for all the CO₂ created within its boundaries.  It is not responsible for the CO₂ created outside its borders, including the  CO₂ emitted during the production of any goods shipped in for consumption or usage inside the city limits.  The one exception is electricity.  We accounted for electricity produced outside of Chapel Hill, but only the exact amount that is generated for use within Chapel Hill's borders.
2.    All roads and transportation data only include the roads within the city of Chapel Hill, as defined by the Chamber of Commerce.  The roads are cut off, and assumed nonexistent, at the city limits of Chapel Hill, even if the road, as well as the operation of any vehicles, continues outside of this specified area.
3.    Our definition of Chapel Hill includes a part of the ocean.  Since the mixing ocean is the largest Carbon sink in the world, and since the amount of Carbon emitted over the ocean is negligible, it is assumed that each acre of land should be accompanied with its fair share of the world's oceans.  This calculation is completed using the ratio of Chapel Hill's land area to the total land area of the Earth.
4.    Our model also attributes a portion of the planet's soil to Chapel Hill, since this is another important Carbon sink.  This amount of soil is also calculated from the ratio of Chapel Hill's land area to the total land area of the Earth.  It is therefore assumed that the carbon sequestering ability of all the soil in the world is uniform.
5.    We assume that the Carbon sequestering ability of the flora in North Carolina is uniform.  Obviously, a deciduous forest will have a very different sequestering ability than a coastal wetland, but that is a difference that will be left to the investigation of future capstone classes.  The proportion of flora attributed to Chapel Hill, along with the net primary productivity of this flora, was calculated from an average value of the net primary productivity of North Carolina, multiplied by the surface area of Chapel Hill.
6.    We attributed a certain fraction of the total Carbon released from deep Earth activities like volcanoes to Chapel Hill.  This amount was also calculated using the proportion of Chapel Hill's land area to the total land area of the Earth.
7.    Specifically for Chapel Hill's intentions, the contribution of industry to Carbon emissions is assumed to be zero.  The true amount is negligible enough that we did not include it in our calculations.
8.    Our model assumes that propane is not a significant source of energy for the people of Chapel Hill.  We found that the amount of energy derived from propane is minimal enough not to be considered in our calculations.
9.    The amount of Carbon released per unit of fuel type was not specifically investigated by our group.  The default values included when Stella was created were not changed, and therefore are assumed to be the same as they were in the early 1990's.
10.    The ultimate goal of double the pre-industrial level of CO₂ in the atmosphere was identified by multiplying the default goal of 1160 Billion metric tons of Carbon by the fraction of Chapel Hill's land area over the total land area of the Earth.  It was then multiplied by 4, so as to account as well for the atmosphere located directly above the portion of the mixing ocean which has been allotted to Chapel Hill.
11.  This is an ongoing project.  We acknowledge that some of these variables may be investigated further and reported with more accuracy, but would like to iterate the fact that we have been working on a limited time schedule, and cannot even attempt to complete every aspect of the CRed project by ourselves during one semester.